A novel high-pressure phase of ScN5with higher stability predicted from first-principles calculations.

For binary compounds of Sc-N, the stable structures and stoichiometries were studied from ambient condition to high pressure of 100 GPa, adopting CALYPSO method. The newly predictedP21/c-ScN5compound was more energetically stable under high pressureP= 62 GPa comparing with the three previously reported phases ofP1-ScN5,Cm-ScN5andC2/m-ScN5. Furthermore, the high-pressure phase ofP21/c-ScN5was dynamically stable at ambient condition, so the ambient-pressure recovery is possible. In this paper, the study suggested that the energetic polynitrides can be obtained in transition metal nitrides under high pressure. And we identified one novel 3D extended puckered poly-nitrogen network in theP21/c-ScN5structure, which is similar to theC2/m-ScN5. The decomposition ofP21/c-ScN5to ScN and N2under ambient pressure was estimated to release 5.02 eV energy per formula unit (f.u.), corresponding to 4.19 kJ g-1in energy density, which was expected to be highly exothermic. The present results can conduce to obtain more polynitrogen forms and theoretically encourages experimental discovery in these promising materials.